Understanding language is one of the most fundamental human cognitive abilities. It plays an important role in normal development, and is a major means for acquiring information in many domains. Psycholinguists have made significant progress in clarifying the structures and processes that underlie language comprehension. In recent years, it has become clear that a central issue in this area is lexical access. Theories must specify how the presentation of a spoken word leads to a particular lexical representation becoming activated, and what the effects of such activation are: What effect does one active lexical representation have on others, and on units at other levels of representation? The current proposal includes a large set of theoretically-driven empirical tests of the basis of lexical activation, and especially, of the consequences of lexical activation. The experiments use a range of different methodologies, in order to assure correct theoretical inferences through converging operations. The tests include analyses of the rise, peak, and fall of lexical activations, and investigations of the perceptual effect that active lexical representations can have on other lexical representations, and on sublexical encoding. The experiments test for both excitatory and inhibitory influences on these other representations. The product of the proposed research will be a much better understanding of the architecture of the system that accomplishes language comprehension. Such an understanding is critical to our understanding language processing. In turn, because language is such a fundamental cognitive ability, progress in describing language processing will enhance our understanding of human cognition.